The present invention relates to aryl ketone containing iodonium salts, their method of synthesis and their use as photoinitiators in photopolymerizable organic materials.
Prior to the present invention, as shown by Smith U.S. Pat. No. 4,378,277, diaryliodonium salts, such as diphenyliodonium hexafluoroarsenate, were used as photoinitiators for effecting the cationic polymerization of epoxy resins. Although the aforementioned diaryliodonium salts were effective in converting epoxy resins to the tack-free state in a relatively short period of time, it was often difficult to achieve a cured epoxy resin product having a satisfactory thickness because the cured film often acted as a barrier to the ultraviolet light required to activate the diaryliodonium salt. Improved thickness of cure was achieved by employing certain arylsulfonium salts, as shown by Smith U.S. Pat. No. 4,173,476. It would be desirable to achieve deeper section cures with UV polymerizable organic materials employing diaryliodium salts in particular applications.
The present invention is based on our discovery that aryl ketone containing diaryliodonium salts having the formula, EQU [RR.sup.1 I].sup.+ X.sup.- ( 1)
where R is a C.sub.(6-13) monovalent aromatic hydrocarbon radical or halo substituted monovalent aromatic hydrocarbon radical and R.sup.1 is a monovalent aryl ketone group which is attached to iodine by a nuclear carbon atom, and X.sup.- is a counter ion, can be used with a wide variety of photopolymerizable organic materials such as epoxy resins, to make deep section photopolymerizable organic materials. The aryl ketone containing diaryliodonium salts of formula (1), can be made by a simple metathesis between a diaryliodonium tosylate precursor and an appropriate counter ion source, such as a hexafluoro metal or metalloid salt. The diaryliodonium tosylate salt precursor can be made by the direct condensation of an aryl iodosotosylate with an aromatic ketone in accordance with the following equation, where Tos.sup.- is tosylate: ##STR1## where R and R.sup.1 are as previously defined. A synthesis of diaryliodonium salts involving the direct condensation of aryliodosotosylates has been reported by Koser, Wettach and Smith, Journal of Organic Chemistry, 45, 1944 (1980). As indicated above, conversion of the aryl ketone containing aryliodoniumtosylates to aryl ketone containing diaryliodonium salts of formula (1), can be achieved by a simple metathesis as shown by the following equation: EQU [RR.sup.1 I].sup.+ Tos.sup.- +MX.fwdarw.formula (1)+M Tos.sup.-
where M is a metal or metalloid.